Automatic speed control or so-called cruise control devices have been widely used on vehicles, particularly automobiles. In general, they comprise a direct throttle connection controlled by an electronic circuit utilizing an actual speed sensor input such as a device that measures the rpm's of the vehicle driveshaft. Normally, once the speed control is activated, it is deactivated only by a direct switch-off or by activation of the vehicle brake.
For various safety and economic reasons, all automatic speed controls heretofore devised are intended to disengage when the vehicle brake is applied. That is, they will disengage if everything in the vehicle brake circuit and the speed control circuit functions properly. However, the method of detecting the application of the vehicle brake and the lack of an adequate functional safety backup in prior cruise controls greatly decreased their overall safety and reliability. Prior to the present invention, no cruise control system available could insure that no conceivable combination of failures could occur in the vehicle brake circuit or in the speed control that would prevent the speed control from becoming disabled when necessary.
Typical prior art speed control systems detect the brake application by attaching a single wire to the lamp side of the vehicle brake switch. When the brake is applied, this wire becomes "hot" and sends a signal to the speed control circuit to disengage. This method of brake detection is simple but highly unreliable. For example, if the vehicle is towing a trailer, it is not uncommon for the extra load on the brake and turn signal circuits to occasionally blow the fuse. If this happens, when the brake is applied, there will be no "hot" signal to the speed control and it will remain engaged. As the vehicle slows down, the speed control will attempt to regain the speed by opening the throttle. In addition, the extra weight of the trailer reduces the vehicle's braking capacity, creating a very dangerous situation. One suggested solution to this problem was to add a second independent switch to the brake pedal. This was satisfactory for demonstrations but the number of mechanical adaptors required for after-market installations made it unmanageable. A more practical solution was to monitor the "hot" side of the brake switch to determine if the fused side of the circuit was in proper order. However, this alone was still not sufficient because the connections to the brake wires were typically made with wire tap connectors that snap over the wires and pierce the insulation with a sharp point or knife edge. While these connectors were usually quite reliable, they often failed. For example, if the installer did not use the proper size connector, the connectors often popped off (if the connector was too small) or made intermittent contact (if the connector was too large). Also, in the case of the above circuit, if the hot wire connector failed, then the cruise control would disengage, but if the lamp connector failed, there was no signal to send to the control to disengage it.
Another possibility for failure which arose in prior cruise control systems, although less common than either of the above two failures, was that the switch itself would jam, freeze, or physically break. This prevented the brake signal from getting to the speed control circuit even though the remaining circuits were in working order. To detect the application of the brake when the electrical circuits had failed, an auxillary "redundant brake" circuit was added to detect the deceleration of the vehicle below the desired cruise speed by a preset threshold. At least one prior art design used this approach to create a redundant brake detection, but had the disadvantage of becoming disabled in the resume mode, that is, a situation where the vehicle slowed down below its set speed and then attempted to regain that set speed. Since the resume mode can be selected well below the redundant brake threshold, it must be disabled to allow the vehicle to return to the cruise speed. However, the most vulnerable time for a brake circuit malfunction is immediately after slowing down or coming to a stop and then selecting the resume mode. This is the time the redundant brake is needed the most.
It is, therefore, an object of the present invention to provide a cruise control disengaging system on a vehicle that will monitor the state of the vehicle brake system and automatically disengage the speed control should the brake fuse burn out.
Another object of this invention is to provide a system that will monitor the state of a vehicle brake system and disengage the speed control of the vehicle should any of the wires become disconnected.
Yet another object of this invention is to provide a system that will monitor the speed of the vehicle at all times to provide a redundant brake detection should the vehicle brake circuit fail in such a way that the aforementioned portions of the system become ineffective.
Another object of this invention is to provide a redundant brake system that will function equally as well in the resume mode as it does in the cruise mode.